In biomedical applications, it has become important to deliver small quantities of liquids through the stratum corneum of humans into the underlying tissue or also to sample fluids from the underlying tissue. For this purpose, micro-needles have been developed. Due to their small dimensions they can be inserted into the skin without pain and cause less tissue damage than conventional hypodermic needles. In the field of transdermal and/or intradermal application the micro-needles have the potential to become the preferred drug delivery device.
Micro-needles are usually split in two main categories: solid or hollow micro-needles. Solid micro-needles do not in principle allow an active administration of a substance such as a drug but rather use a coating of the needle to deliver the substance through the skin.
In the case of hollow needles, they have a channel or lumen that is able to direct the substance through the skin. Different hollow out-of-plane micro needle for transdermal and/or intradermal applications have been described in the past. They are usually arranged in two dimensional arrays to decrease flow resistance through the device. The array can be achieved with wafer level processing. The openings are at the top of the needle, a design that increases the risk of clogging or coring. Examples of such needles are disclosed for example in the following patents: U.S. Pat. No. 6,132,755 and U.S. Pat. No. 6,334,856, the content of which is incorporated by reference in its entirety in the present application.
Other different designs exist for example with a traversing hole opening at the tip of the needle (see for example D. V. McAllister et al. <<Microfabricated needles for transdermal delivery of macromolecules and nanoparticles: fabrication methods and transport studies>>, Proc. Natl. Acad. Sci. U.S.A, vol. 100, no. 24, pp. 13755-60, 2003) or to a side as disclosed in WO 02/17985 or in US 2004/0267205 and in WO 03/015860, all entirely incorporated by reference in the present application
More specifically, patent publications US 2004/0267205 and WO 03/015860, corresponding to EP 1 416 996 (all entirely incorporated by reference in the present application) disclose micro-needles and a method for manufacturing said micro-needles. According to these publications, the micro-needle usually protrudes from a support member and comprises a micro-needle body portion, a closed pointed tip portion closing off a lumen in the tip region, and a cylindrical inner lumen extending through said support member and into said protruding needle. The needle body portion has at least one side opening communicating with said inner lumen, and the exterior envelope surface of the needle structure intersects the envelope surface of the cylindrical inner lumen within the needle structure in at least one defined region, so as to create at least one side opening in said body.
Such micro-needles and other known ones have one single inner lumen for the drug passage and one or several openings for the drug administration itself. Even if they have several openings, they still have one single supplying lumen. In case of obstruction for example by a particle or a part of the skin, a common risk considering the sizes of these needles, the needle becomes then useless. The single hole also has either a small diameter, thus a high flow resistance, or a large diameter making the needle more fragile.
Micro-blades with several lumens are disclosed in US 2009/0093776 A1. They however don't show a tip at their distal end but a blade. The related openings are furthermore not designed (and may not be used) for a tip.
Micro-needles with several lumens are disclosed in US 2004/0164454 A1. Their openings are however oriented in a way that the risk of obstruction is very high.